An operating system (OS) acts as an intermediary between users and computer hardware by controlling and coordinating hardware and software resources. The document discusses the components of a computer system including hardware, OS, application programs, and users. It describes the functions of an OS as a resource allocator and control program. Early batch systems had long turnaround times due to lack of parallelism between CPU and I/O operations. Multiprogramming systems improved efficiency by running multiple programs simultaneously using interrupts. Timesharing systems provided further interactivity through rapid context switching between user programs. Personal computing systems prioritized user convenience with single-user, portable devices.

1. OPERATING SYSTEMS
COCHIN UNIVERSITY COLLEGE OF ENGINEERING KUTTANADU
DAY1

2. What is an os?
● An OS is a program that acts an intermediary between the user
of a computer and computer hardware.
● Major cost of general purpose computing is software.
● OS simplifies and manages the complexity of running application
programs efficiently.

3. Computer System Components
● Hardware
● Provides basic computing resources (CPU, memory, I/O devices).
● Operating System
● Controls and coordinates the use of hardware among application programs.
● Application Programs
● Solve computing problems of users (compilers, database systems, video games, business programs such
as banking software).
● Users
● People, machines, other computers

4. Principles of Operating Systems -
Lecture 1 4
Abstract View of System
System and Application Programs
Operating System
Computer
Hardware
User
1 User
2
User
3
User
n
compiler assembler Text editor Database
system
...

5. Principles of Operating Systems -
Lecture 1 5
Operating System Views
● Resource allocator
● to allocate resources (software and hardware) of the
computer system and manage them efficiently.
● Control program
● Controls execution of user programs and operation of I/O
devices.
● Kernel
● The program that executes forever (everything else is an
application with respect to the kernel).

6. Computer System Architecture
(traditional)

7. Principles of Operating Systems -
Lecture 1 7
Operating System Spectrum
● Monitors and Small Kernels
● special purpose and embedded systems, real-time systems
● Batch and multiprogramming
● Timesharing
● workstations, servers, minicomputers, timeframes
● Transaction systems
● Personal Computing Systems
● Mobile Platforms, devices (of all sizes)

8. Simple Batch Systems
(1960’s)
● Reduce setup time by batching jobs with similar requirements.
● Add a card reader, Hire an operator
● User is NOT the operator
● Automatic job sequencing
● Forms a rudimentary OS.
● Resident Monitor
● Holds initial control, control transfers to job and then back to monitor.
● Problem
● Need to distinguish job from job and data from program.
Principles of Operating Systems -
Lecture 1 8
From John Ousterhout slides

9. Principles of Operating Systems -
Lecture 1 9
Supervisor/Operator Control
● Secure monitor that controls job processing
● Special cards indicate what to do.
● User program prevented from performing I/O
● Separate user from computer
● User submits card deck
● cards put on tape
● tape processed by operator
● output written to tape
● tape printed on printer
● Problems
● Long turnaround time - up to 2 DAYS!!!
● Low CPU utilization
• I/O and CPU could not overlap; slow mechanical devices.
IBM 7094
From John Ousterhout slides

10. Principles of Operating Systems -
Lecture 1 10
Multiprogramming
● Use interrupts to run multiple programs
simultaneously
● When a program performs I/O, instead of polling, execute
another program till interrupt is received.
● Requires secure memory, I/O for each program.
● Requires intervention if program loops
indefinitely.
● Requires CPU scheduling to choose the next job
to run.

11. Principles of Operating Systems -
Lecture 1 11
Timesharing (cont.)
● Interactive (action/response)
● when OS finishes execution of one command, it seeks
the next control statement from user.
● File systems
● online filesystem is required for users to access data and
code.
● Virtual memory
● Job is swapped in and out of memory to disk.

12. Principles of Operating Systems -
Lecture 1 12
Personal Computing Systems
● Single user systems, portable.
● I/O devices - keyboards, mice, display screens, small
printers.
● Laptops and palmtops, Smart cards, Wireless devices.
● Single user systems may not need advanced CPU
utilization or protection features.
● Advantages:
● user convenience, responsiveness, ubiquitous
Hardware – cheap ; Human – expensive

13. Computer System Organization
13
I/O devices

14. Syllabus plan
1.Introduction
2.Process management
3.Memeory management
4.Filemanagement
5.i/o management